You might at first. But then your body decides that there is a famine going on. It will slow any non essential functions to make sure that there is enough energy for the esential ones. It will use as few calories as possible, storing what it can as fat in case the famine gets worse. It will also resist losing what precious fat stores it has.

Remember you need so many calories a day just to survive. Blood transfer, tissue regeneration, active cell transport, breathing, repairing muscle and vital organs, all of this takes energy a.k.a. calories. When you go to low your body gets to decide which of those aren't as important as the others